Ozone is a very strong oxidant. Disinfection property, discoloration effect, and deodorization effect which derive from the oxidizing ability are applied in various fields. A disinfection method and a discoloration method utilizing ozone can be processing methods in which secondary pollution does not have to be concerned, because ozone can be readily decomposed into oxygen spontaneously. Ozone, dissolved in water, increases the oxidizing ability, and is generally used for disinfection and the like. For these purposes, developing a production method is required wherein ozone gas or ozone-water can be more easily and more effectively produced.
As for a method to produce gaseous ozone, UV lamp method, silent discharge method, and electrolysis method are known (for example, see Non-patent Document 1). The UV lamp method, wherein a small amount of ozone is produced, is usually used for removing a small amount of odor, such as for deodorizing a room or a car. The silent discharge method is a general method for producing ozone gas. However, when atmospheric air is used as the ingredient, nitrogen oxide is simultaneously produced. In order to prevent this, oxygen gas should be used as the ingredient, or an attachment device, which concentrates only oxygen in atmospheric air, should be equipped. Moreover, impurity incorporation also becomes a problem wherein metal impurity gets mixed in ozone gas due to a metal electrode being worn away. In contrast, ozone gas can be obtained by water electrolysis. Although the ozone gas obtained by the electrolysis method contains moisture, ozone gas with high purity and high concentration can be easily obtained.
As for a method to obtain ozone-water, some methods are known wherein ozone gas, obtained by the above-described methods, is dissolved in water, or wherein ozone-water is produced directly by the electrolysis method. Ozone-water could be obtained by running ozone gas, produced according to the silent discharge method or the electrolysis method, through a vapor-liquid dissolution tower and dissolving the ozone gas in water. However, a device for this kind of method would become large and complicated. On the other hand, according to the electrolysis method, wherein an electrolysis cell is constituted with a porous or mesh anode and a porous or mesh cathode interposing a solid polymer film therebetween, and the cell is used so as to electrolyze tap water or purified water, ozone-water can be directly produced. Moreover, a device for this kind of method can be easily small.
The materials used for an electrode for producing ozone gas or ozone-water by the electrolysis method, are generally lead dioxide and platinum, because of their prominent catalytic functions. These materials are formed into a porous or mesh anode 3, and used together with a suitable cathode 5 interposing a solid polymer film 7 therebetween. As a result, an electrolysis cell 1, shown, for example, in FIG. 1, is constituted. Ozone gas or ozone-water can be obtained by supplying purified water or tap water in an anode chamber 13 of the electrolysis cell 1 (see, for example, Patent Documents 1 and 2).
However, in a case, such as in Patent Documents 1 and 2, wherein lead dioxide and platinum are used for the electrode, a problem has been pointed out that the electrode gets worn away and dissolved, as the electrode is used in electrolysis for producing ozone. Particularly, when lead dioxide is used for the electrode, there is a possibility that lead gets mixed into ozone-water even in minute amount. Therefore, use of the ozone-water directly produced by the electrolysis is not preferable. Instead, some methods are used so as to process the ozone-water, obtained by the electrolysis, by separating ozone by using a vapor-liquid separator so as to obtain ozone gas, and furthermore by running the obtained ozone gas through a gas dissolution tower and dissolving the ozone gas into water so as to obtain ozone-water. As a result, an ozone generator tends to become large in size, complicated, and expensive. Moreover, since the state of lead dioxide is easily changed and the ability to produce ozone tends to be decreased, prevention is required by constantly applying voltage on an anode for anodic polarization. Therefore, an ozone generator needs to be equipped with an extra power supply for in case of emergency. An ozone generator still becomes large, complicated, and expensive.
Platinum is used as a relatively stable material for an electrode. However, the fact is known that platinum gradually gets worn away and dissolved in electrolysis wherein large electric current and high voltage is applied. Therefore, a platinum electrode needs to be regularly replaced. Moreover, platinum is rare noble metal and expensive. This fact becomes an obstacle for using platinum for an electrode.
Recently, a diamond film with electric conductivity is suggested as a material for an electrode in place of the above-described materials. The principal characteristics of the conductive diamond film include unique characteristics which cannot be seen in other materials for an electrode: for example, the conductive diamond film has high mechanical strength and high chemical inertness; molecules are not easily adsorbed to the diamond film, the diamond film exhibits a wide potential window in which oxidative decomposition and reductive decomposition of solvent do not easily occur; there is selectivity of the reaction, and so on. Therefore, producing ozone has been considered by using the diamond film. The diamond film is formed on a mesh or porous substrate by the hot-filament chemical vapor decomposition (CVD) or the microwave plasma assisted CVD. The diamond film is utilized as an anode in an electrolysis cell wherein the anode interposes a solid polymer film with a cathode (for example, see Patent Document 3).    Non-Patent Document 1: Sugimitsu, Hidetoshi (February 1996). Basics and Applications of Ozone: Korin    Patent Document 1: Unexamined Japanese Patent Publication No. 1-139785    Patent Document 2: Unexamined Japanese Patent Publication No. 1-312092    Patent Document 3: Unexamined Japanese Patent Publication No. 9-268395